#in brackets I wrote the full height of the sprites

[yon-shi]

Undertale characters' height (in pixel)

* Flowey - 20 pixels (21 with all petals)

* Monsterkid - 25 pixels (27 with spikes)

* Asriel - 28 pixels

* Frisk and Chara - 29 pixels

* Sans - 30 pixels

* Alphys - 28 pixels (31 with spikes or if she’d stop slouching)

* Muffet - 32 pixels (35 with hair and her heels are not too high)

* Napstablook - 33 pixels

* Mad Mew Mew - 39 pixels (41 with ears)

* Mettaton - 42 pixels (45 with surface)

* Papyrus - 42 pixels

* Undyne - 47 pixels (54 with hair)

* Mystery man- 48 pixels

* Mettaton EX - 52 pixels

* Toriel - 50 pixels (52 with horns)

* Asgore - 54 pixels (61 with horns)

Bonus

And version without background if you need it for whatever reason